On the Divergence of Alleles in Nested Subsamples from Finite Populations

Within-population variation at the DNA level will rarely be studied by sequencing of loci of randomly chosen individuals. Instead, individuals will usually be chosen for sequencing based on some knowledge of their genotype. Data collected in this way require new sampling theory. Motivated by these observations, we have examined the sampling properties of a finite population model with two mutation processes and with no selection or recombination. One mutation process generates new alleles according to an infinite-alleles model, and the other generates polymorphisms at sites according to an infinite-sites model. A sample of n genes is considered. The stationary distribution of the number of segregating sites in a subsample from one of the allelic classes in the sample conditional on the allelic configuration of the sample is studied. A recursive scheme is developed to compute the moments of this distribution, and it is shown that the distribution is functionally independent of the number of additional alleles in the sample and their respective frequencies in the sample. For the case in which the sample contains only two alleles, the distribution of the number of segregating sites in a subsample containing both alleles conditional on the sample frequencies of the alleles is studied. The results are applied to the analysis of DNA sequences of two alleles found at the Adh locus of Drosophila melanogaster. No significant departure from the neutral model is detected.     

Feasibility of automating the micronucleus assay

The results of a feasibility study on the automation of the micronucleus assay in whole blood cultures of human lymphocytes are reported. The assay requires determination of the number of lymphocytes with micronuclei among the proliferating population. Using an in-house-assembled image analysis system, a prototype software package was developed that addressed two problems: micronuclei identification and discrimination of nonproliferating cells from proliferating lymphocytes (the only ones that can give rise to micronuclei). The results of manual verification of automated micronucleus scoring showed that 70% of all digitized micronuclei were extracted from the images and 90% of them were correctly classified and paired with a parent nucleus by an "affinity function". The discrimination between proliferating and nonproliferating cells was carried out by linear discriminant analysis of simple nuclear features extracted from Feulgen-stained cells. Among the Feulgen-stained nuclei that were identified by autoradiography as proliferating or not, 85% were correctly classified by a six-feature discriminant function.     

Subtidal algal colonization following the removal ofEchinus

Summary 1. On the seaward face of Port Erin breakwater large algae do not occur on the lowest three metres. Here the density ofEchinus esculentus is high.2. Over a three year period allEchinus were removed from a 10 m wide strip at about monthly intervals. The total number of individuals removed approached 3000.3. One year after initial clearance the mean density ofLaminaria hyperborea sporelings on the strip was 22.7/m² and 5.1/m² to one side of it. By the winter these had almost disappeared outside the strip and in the succeeding years second and third year plants were found only on the strip or close to its edge. Other algae were similarly affected.4. It is concluded that the lower limit ofL. hyperborea is determined at least in part by the grazing pressure ofEchinus and that the urchins exercise some control over the numbers of other algae.

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Algenkolonisation im untergetauchten Gezeitenbereich nach Entfernung vonEchinus

Kurzfassung An der Sesseite des Port Erin Wellenbrecherdammes kommen keine größeren Algen im Bereich der unteren 3 m vor. Hier herrscht eine große Besiedlungsdichte des SeeigelsEchinus esculentus (3,6 Individuen pro m²). Über eine Zeitspanne von 3 Jahren wurden nun sämtlicheE. esculentus von einem 10 m breiten und 12 m langen Felsstreifen allmonatlich entfernt; insgesamt wurden dabei etwa 3000 Individuen abgesammelt. Ein Jahr nach Beginn des Absammelns betrug die mittlere Siedlungsdichte der jungenLaminaria hyperborea auf dem von Seeigeln freigehaltenen Felsstreifen 22,7/m². In den folgenden Jahren wurden zwei- und dreijährigeL. hyperborea nur auf diesem Felsstreifen oder in der Nähe seiner Begrenzungen gefunden. Andere Algenarten reagierten in ähnlicher Weise. Aus den Befunden wird gefolgert, daß die untere Verbreitungsgrenze vonL. hyperborea zumindest zum Teil durch Seeigelfraß bestimmt wird, und daßE. esculentus die Siedlungsdichte der anderen Algenarten beeinflußt.

     

A serological comparison of the three morphological phases of Coccidioides immitis; complement fixation tests with anti-Histoplasma capsulatum serum

Summary The results of this study indicated that antigens prepared from the three morphological phases ofCoccidioides immitis differed in their complement fixing activity with anti-Histoplasma capsulatum pooled serum. Spherule antigens were serologically less active in tests with the anti-H. capsulatum pooled serum than antigens prepared from arthrospores and from mycelium.Antigenic determinants which are common toC. immitis andH. capsulatum appeared to be located on the intact arthrospore cellular surface but not on the surface of spherule cells.Part of a dissertation submitted to the Graduate School of Duke University in partial fulfillment of requirements for the Ph. D. degree.This work was supported by contract with the Department of the Army, Fort Detrick, Frederick, Maryland.In conducting the research reported herein, the investigators adhered to Guide for Laboratory Animal Facilities and Care established by the Committee on the Guide for Laboratory Animal Facilities and Care of the Institute of Laboratory Animal Resources, NAS-NRC.     

Vitamin K-dependent gamma-carboxylation of the 1,25-dihydroxyvitamin D3 receptor.

It has been reported that vitamin K deficiency in the rat markedly increases the 1,25-dihydroxyvitamin D3 receptor (VDR) binding to DNA and that vitamin K-dependent gamma-carboxylation of endogenous substrates of the intestinal and renal cytosol, also containing VDR, sharply reduced that binding (Sergeev, I.N., and Spirichev, V.B. (1989) Nutr. Res. 9, 725-733). In the present study we have evaluated vitamin K-dependent 14CO2 incorporation to VDR quantitated by immunoprecipitation with anti-VDR monoclonal antibodies. The results obtained strongly suggest that VDR in vitro can undergo gamma-carboxylation in the presence of vitamin K1 and that 15-25% of Glu residues in the VDR are carboxylated in vivo. Taking into account our earlier findings, it is likely that the VDR gamma-carboxylation modulates its binding to DNA.     

Developmental regulation of pectic polysaccharides in the root meristem of Arabidopsis

JIM 5, an antibody that recognizes a relatively unesterifiedpectic epitope, distinguishes between dividing (meristematic)and non-dividing (central cells of the quiescent centre) cellsin the Arabidopsis root tip, indicating that non-dividing cellwalls contain higher levels of relatively unesterified pectinthan dividing cells. JIM 7, an antibody that recognizes a relativelymethyl esterified epitope, labels all cell walls uniformly throughoutthe root, suggesting that there is little variation in the relativelymethyl esterified pectic component in the two cell types. Theseobservations suggest that the characteristics of cell wallsin the root tip result in part from modulations in the amountof unesterified and non-methyl esterified pectin. Key words: Pectin, quiescent centre, roots, Arabidopsis     

An in situ assay for induced diphtheria-toxin-resistant mutants of diploid human fibroblasts

The sensitivity of diploid human fibroblasts to the cytotoxic effects of diphtheria toxin (DT) depended on the cell growth status. Exponentially growing cells treated with 10^?3-1 lethal flocculating units (LF) of DT/ml for 4 days survived with a frequency of 4 × 10^?4. However, the DT-resistant phenotype of colonies isolated under these conditions was not stable. When the growth of the cells had been arrested by confluence or deprivation of serum growth factors prior to treatment with DT (4 days, 10^?3-0.6 LF/ml), the survival decreased to 2 × 10^?6 and the resistance of isolated colonies was stable. An in situ assay for induced DT-resistant mutants was developed in order to avoid problems associated with the possible reduced viability of the mutants relative to that of wild-type cells. A reproducible and linear dose response was obtained for the induction of DT-resistant mutants by ethylnitrosourea. The mutants were induced with high frequency by this compound (e.g., 10^?3 mutants/viable cell at a 37% survival dose); complete expression of the mutant phenotype occurred after 6 generations of growth under nonselective conditions. Isolated mutant colonies showed stable resistance to DT and were cross-resistant to Pseudomonas aeruginosa exotoxin A.     

Accessibility of sialo components in a murine tumor cell to extracellular N-acetylneuraminate glycohydrolase (sialidase)

Lipid-bound sialic acid in the murine melanoma cell is not totally inaccessible to an exogenous macromolecular probe, as formerly believed. Roughly 30% of the sialic acid bound to lipid, and an equal proportion of the sialic acid bound to protein is cleaved by the action of Clostridium perfringens$\text{N-}\text{acetylneuraminate}$ glycohydrolase (neuraminidase, sialidase) when the purified enzyme is added to the suspension medium of intact murine melanoma cells freshly derived from the tumor. Cleavage of lipid-bound sialic acid is indifferent to the presence of Ca²⁺ in the medium. However, maximum release from protein requires a physiological concentration of this divalent cation. Variation in ionic strength has no effect on release of sialic acid. These findings show that a restricted portion of the bound sialic acid may be released from the intact murine melanama cell by the extracellularly supplied enzyme acting topographically.